Explosive device for perforating high-strength metal plates

ABSTRACT

1. An explosive device for removing a circular pluglike fragment from a metal plate structure, comprising; A. CYLINDRICAL METAL OUTER CASING TUBE HAVING FRONT AND REAR ENDS AND CONTAINING A CHARGE OF EXPLOSIVE MATERIAL, B. SAID CHARGE HAVING A FIRST, CYLINDRICAL, AXIAL PORTION IN CIRCUMFERENTIAL CONTACT WITH THE INNER SURFACE OF THE WALL OF SAID TUBE AND EXTENDING FORWARDLY TO A CIRCULAR FORWARD LIMIT OF EXPLOSIVE CHARGE AND TUBE CONTACT, AND HAVING A SECOND, FRONT END, AXIAL PORTION ADJOINING AND EXTENDING FORWARDLY FROM SAID CIRCULAR FORWARD LIMIT AND TERMINATING AT ITS FORWARDMOST PORTION AT AN AXIAL POSITION SUBSTANTIALLY COADJACENT THE FRONT END OF THE TUBE, SAID FRONT END AXIAL PORTION FORMING AN AXIALLY ALIGNED FORWARDLY CONVERGING BODY OF REVOLUTION HAVING ITS OUTER SURFACE IN RADIALLY SPACED RELATIONSHIP TO THE WALL OF THE TUBE DEFINING AN ANNULAR CAVITY THEREABOUT BETWEEN THE BARE OUTER SURFACE OF THE EXPLOSIVE MATERIAL AND THE INNER SURFACE OF THE WALL OF SAID TUBE, SAID ANNULAR CAVITY BEING OF FORWARDLY INCREASING CROSS SECTION FORMING AN EXPLOSIVE PRESSURE FOCUSING CAVITY FOR CONCENTRATING THE INITIAL EXPLOSIVE EFFECT IN AXIALLY FORWARDLY AND LATERALLY OUTWARD DIRECTIONS TO PRODUCE A SEMITOROIDAL CRATER HAVING A MEDIAN CRATER DIAMETER APPROXIMATELY COEXTENSIVE WITH THE DIAMETER OF THE TUBE IN THE SURFACE OF A METAL TARGET PLATE DISPOSED ADJACENTLY AND NORMALLY TO THE FRONT END OF THE TUBE AT THE TIME THE CHARGE IS EXPLODED, C. SAID CHARGE BEING MADE OF AN EXPLOSIVE MATERIAL OF SUCH A CHARACTER THAT IT PRODUCES A TIME DISTRIBUTION OF DYNAMIC EXPLOSIVE LOADING EFFECTS BY WHICH THE HIGH LEVEL OF EXPLOSIVE LOADING IS SUSTAINED MOMENTARILY AFTER FORMATION OF THE SEMITOROIDAL CRATER TO PRODUCE A PUNCHLIKE EXPLOSIVE LOADING UPON THE SURFACE OF THE TARGET PLATE ENCIRCLED BY THE CRATER TENDING TO CAUSE AN APPROXIMATELY FRUSTOCONICAL FRACTURE SURFACE EXTENDING FROM THE BOTTOM OF THE CRATER TO THE OPPOSITE SIDE OF THE PLATE AND DIVERGENT IN THE DIRECTION TOWARD SAID OPPOSITE SIDE, WHEREUPON THE PORTION OF THE PLATE ENCOMPASSED BY THE CRATER AND FRACTURE SURFACE IS REMOVED FROM THE BODY OF THE PLATE.

United States Patent [72] Inventors John Pearson;

William B. McLean; Lawrence N. Cosner, all of China Lake, Calif. [21]Appl. No. 413,678 [22] Filed Nov. 20, 1964 [45] Patented Oct. 19, 1971[73] Assignee The United States of America as represented by theSecretary of the Navy 7 [54] EXPLOSIVE DEVICE FOR PERFORATING HIGH-STRENGTH METAL PLATES 5 Claims, 4 Drawing Figs.

[52] US. Cl 102/24 [51] Int. Cl F42b H00 [50] Field of Search 102/22,23, 24 HQ 56, 98

[56] References Cited UNITED STATES PATENTS Re. 23,211 3/1950 Mahaupt102/22 X 2,988,994 6/1961 Fleischer 102/24 I-IC 3,117,518 1/1964 Porteret a1, 102/24 l-IC FOREIGN PATENTS 1,231,003 4/1960 France 102/24 l-ICPrimary ExaminerVerlin R, Pendergrass Att0rneys-G. J. Rubens, V. C.Muller and P. H. Firsht b. said charge having a first, cylindrical,axial portion in circumferential contact with the inner surface of thewall of said tube and extending forwardly to a circular forward limit ofexplosive charge and tube contact, and having a second, front end, axialportion adjoining and extending forwardly from said circular forwardlimit and terminating at its forwardmost portion at an axial positionsubstantially coadjacent the front end of the tube, said front end axialportion forming an axially aligned forwardly converging body ofrevolution having its outer surface in radially spaced relationship tothe wall of the tube defining an annular cavity thereabout between thebare outer surface of the explosive material and the inner surface ofthe wall of said tube, said annular cavity being of forwardly increasingcross section forming an explosive pressure focusing cavity forconcentrating the initial explosive effect in axially forwardly andlaterally outward directions to produce a semitoroidal crater having amedian crater diameter approximately coextensive with the diameter ofthe tube in the surface of a metal target plate disposed adjacently andnormally to the front end of the tube at the time the charge isexploded,

c. said charge being made of an explosive material of such a characterthat it produces a time distribution of dynamic explosive loadingeffects by which the high level of explosive loading is sustainedmomentarily after formation of the semitoroidal crater to produce apunchlike explosive loading upon the surface of the target plateencircled by the crater tending to cause an approximately frustoconicalfracture surface extending from the bottom of the crater to the oppositeside of the plate and divergent in the direction toward said oppositeside,'whereupon the portion of the plate encompassed by the crater andfracture surface is removed from the body of the plate.

PATENTEuum 191971 3,613,581

FIG. 3.

B W "56 R;

F|G 4 dfitaw PEARSO LIAM B. MC LEAN LAWRENCE N. COSNER BY V. C. MULLERATTORN EY.

EXPLOSIVE DEVICE FOR PERFORATING HIGH- STRENGTH METAL PLATES Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This invention relates to a novel-shaped charge device, and moreparticularly to such a device for producing a circular perforation inrelatively thick, high-strength, metal plate structures.

The possibility of obtaining an efficient explosive device forperforating high-strength steel plate structures is of great importancein the field of military ordnance. It is also ofpotential importance inthe rapidly expanding field of explosive working of metals, which tendsto parallel military ordnance developments. The prior art methods forproducing holes in steel plates include conventional shape chargedevices, i.e. devices having a lined conical cavity at the output end ofa charge, and large blast charges. The disadvantage of the conventionalcharge is that it produces a hole having a diameter which is smallrelative to the diameter of the device. The disadvantage of the blastcharge is the large amount of explosive energy required, and hence thelarge size of the device.

The problem is further aggravated in connection with the type of warheadfor use against high-strength plate structures and which contains afollow-through projectile which is to be pushed through" the perforationto the other side of the plate. The follow-through projectile is itselfexplosive and is fused to detonate after it passes to the other side ofthe plate structure. In these instances it is required that theexplosive effects of the device be such that the follow-throughprojectile may be conveniently disposed in the warhead assembly in alocation where the forces of the initial explosion will push it throughthe perforation formed in the armor. Prior to the present invention, thedesign of follow-through projectile warheads have at best beendifficult. An example, which illustrates the complexity of prior artapproaches to the construction of follow-through projectile warheads, isUS. Pat. No.

One broad aspect of the development leading to the present invention didnot, in fact, originate with the inventors. The broad aspect referred tois that of using an explosive device with an inverted-shaped charge toproduce a hole in a target, some tests having been conducted along thisline in a foreign country during World War II. However, it is believedthat the concept was abandoned before promise of feasibility for anypractical use was demonstrated, and that the specific design details andtarget damage data from these early trails were never published.Moreover, an important feature of the present invention is a discoverywhich allows the present invention to provide a practical and economicalweapon.

As distinguished from these and other prior art devices and unsuccessfulattempts, the objectives of the present invention include provision of:

l. A novel and highly efficient explosive device for perforatingrelatively thick high-strength metal plates.

2. An explosive device in accordance with the previous objective whichproduces a hole having the same order of size as the device.

3. An explosive device in accordance with the first listed objectivewhich is readily adaptable for use with a followthrough projectile.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of one form of invention, shown inposition to perforate a target plate;

FIG. 2 is a diagrammatic illustration showing the modes of target damageexperienced by the target plate in FIG. 1;

FIG. 3 is a modified form of invention; and

FIG. 4A, B, C and D are other modified forms of invention.

Referring now to the drawing and in particular toFlG. l, the first formof invention to be described is an'explosive device 10 comprising acharge 12 of explosive material and a thin cylindrical outer casing'tube 14, of any suitable metal, such as stainless steel.

In choice of material for charge '12, it has been discovered that anexplosive known as composition C-3" provides certain properties desiredfor perforating steel plates. Composition C-3 is a conventionalexplosive composition developed at the time of World War II, and isdescribed at pages 20 l-20'4of the publication Military Explosives, Apr.1955, Department of the Navy Technical Manual TM 9-l9l0, Department ofthe Air Force Technical Order TO llAl-34 The nature of the desiredproperties provided by this explosive will be discussed at a later pointin this specification.

Charge 12 and tube 14 are concentrically aligned about an axis A. Asuitable detonator 16 is affix'ed to charge "at its rear end. The frontend of charge 12 is frustoconically shaped with the bare explosivematerial forming a frustoconical surface 18 and a circular end face 20.Behind its frustoconical front end, charge 12 is cylindrical withitslateral surface in circumferential contact with the inner wall of tube14. Theintersection of conical surface 18 and the inner wall of tube 14forms a circular edge 22 which defines the forward limit of contactbetween charge 12 and tube 14. Circular face 20, which forms theforwardmost portion of charge [2, lies in the same plane as the frontend of tube 14. A cavity 24, having the shape of a volume of revolution,is formed between the casing tube and the frustoconical front end of thecharge, the cavity being bounded on its radially outer lateral side bythe axially straight inner wall of the casing tube, and bounded on itsradially inner lateral side by the forwardly convergent frustoconicalsurface 18. Frustoconical surface 18 has an included angle B, ofapproximately 60. However, this angle may be varied considerably, andparticularly can be increased in value. A range of values found toproduce satisfactory results is between a lower limit of 60 and an upperlimit of One factor limiting the geometry of cavity 24, is that distanceC, between-circular edge 22, and the front end of the tube wall may notexceed a limit at which lateral relief-will be experienced at the rearend of the cavity before a forward concentration of the explosive forcesis effected by the constraining forces of the tube. Such undesiredlateral relief effects are typically experienced if distance C exceedsapproximately 12 inches. It is to be noted that because there is a limitto the axial length of the cavity, the frustoconical shape is apreferred shape for use in applications in which the diameter of thecharge would be large, as for example, in torpedo warhead applicationswhere warheads as large as 20 inches in diameter may be used. With thefrustoconical shape, is a simple matter to keep the axial length ofthe'cavity less than the desired limit by choice of the included angleand diameter of circular face 20.

It will be assumed that the device is disposed over a target plate 26,FIG. 1, of relatively thick mild rolled steel, with the front end oftube 14 resting on the upper face of the plate and with the oppositeregion of the lower face of the plate free from any contact. It is to beunderstood that when device 10 is employed as a component of a warheadassembly, this relative disposition is achieved by suitable fusingconventional in the art. FIG. 2 diagrammatically illustrates plate 26after it has been fragmented by explosion of device 10, but with theremoved fragment replaced in its original position in the body of theplate, so that the metal flow and fracture surfaces caused by theexplosion may be seen. The relative position of device 10 prior toexplosion is shown by phantom lines.

Following the discovery of the particular efiectiveness-of compositionC-3, exhaustive experiments were undertaken to gain a betterunderstanding of the physical processes which are involved. The physicalprocess by which device 10 acts upon plate 26, as presently understood,will now be described by reference to FIG. 2. The metal damageexperienced by the plates includes formation of a circular crater 28whichv is generally semitoroidal in cross section and is disposed withits median diameter approximately under, or slightly radially outwardfrom, the former location of the end of the tube wall. Also, aconcentric fracture surface which is approximately of frustoconicalshape with a 45 included angle, extends from bottom of crater 28 to theopposite side of plate 26. The portion of the plate encompassed by thecrater and fracture surface forms a pluglike fragment 32. Fragment 32is, of course, blown clear of the body of plate 26 under the impact ofthe explosion leaving a circular perforation of minimum diameter D.Fragment 32 also contains internal spalling cavities 34 which run alongthe direction of the grain of the rolled steel plate.

It was found that the fundamental physical mode, which results in theformation of circular crater 28, is metal flow in radially outwarddirection, and that this is produced by the pressure-focusing effect ofcavity 24.

Upon closer examination of the approximately frustoconical fracturesurface 30, it will be seen to include a short segment 30a which extendsin the direction parallel to the direction of the explosive forces, andanother short adjoining segment 30a which extends radially outwardly inthe direction of the grain of rolled plate 26. It was found that theprimary physical mode resulting in such a fracture pattern is failure,in shear, of the metal remaining in the zone between the bottom of thecrater and the opposite side of the plate under a force applied over thearea the plate encompassed by the crater.

Several explosive materials were employed and of these composition C-3proved to be the most effective for producing holes in the target plate.This effectiveness appears to be related to the force-time distributionof the load on the target surface. That is, the cratering and thefracturing are events which occur in sequential order, with thefracturing occurring after a crater of some required depth has beenproduced. Accordingly, the formation of fracture surface 30 is theresult of a loading effect which persists at a high enough force levelfor a sufficient period of time after formation of the crater. Thispersisting load effect acts on the area of the plate encompassed by thecrater and punches out the pluglike fragment 32. While composition C-3demonstrates excellent properties for both cratering and fracturing ofthe target plate, it is to be appreciated that other explosives couldpossess the same degree of capability.

Referring now to FIG. 3, there is illustrated a device 100, like that ofFIG. 1 except that a follow-through projectile 36 is disposed in acentral bore which is formed in the charge and opens into front end ofthe charge. It has been found that device 10a punches out a circularpluglike fragment, in essentially the same manner as the device of FIG.1, and in addition the explosive efi'ects are such that projectile 36 isdelivered to the other side of a target through the perforation formedin the plate.

FIGS. 4A, B, C and D show modified forms of the invention which differfrom that of FIG. 1 in the shape of the front ends of their respectivecharge. In FIG. 4A the charge 120 has a frustoconical front end which isspaced a short axial distance away from the front ends of the tube wall.It has been found that the forwardmost portion of a charge may beaxially spaced away from the front end of tube wall by relatively shortdistances, without appreciably effecting the damage process. There is,however, a critical limit beyond which the device fails to produce thedesired damage effects. In devices having a diameter of 3 inches, thislimit of spacing was found to be of the order of one-half inch. Theflexibility to provide such slight spacing at the front end of thedevice can be of significance in certain ordnance applications, such astorpedo warheads, where it may be desirable to recess acoustic equipmentin the front face of the weapon. Charge 12b, FIG. 4B has a compositelyshaped front end consisting of a frustoconical portion and cylindricalportion; charge 12c, FIG. 4C, has a conically shaped front end forming apointed tip; and charge 12d, FIG. 4D, has a bullet-shaped front end.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachin s. It is therefore to beunderstood that within the scope of t 0 appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

I. An explosive device for removing a circular pluglike fragment from ametal plate structure, comprising;

a. cylindrical metal outer casing tube having front and rear ends andcontaining a charge of explosive material,

b. said charge having a first, cylindrical, axial portion incircumferential contact with the inner surface of the wall of said tubeand extending forwardly to a circular forward limit of explosive chargeand tube contact, and having a second, front end, axial portionadjoining and extending forwardly from said circular forward limit andterminating at its forwardmost portion at an axial positionsubstantially coadjacent the front end of the tube, said front end axialportion forming an axially aligned forwardly converging body ofrevolution having its outer surface in radially spaced relationship tothe wall of the tube defining an annular cavity thereabout between thebare outer surface of the explosive material and the inner surface ofthe wall of said tube, said annular cavity being of forwardly increasingcross section forming an explosive pressure focusing cavity forconcentrating the initial explosive effect in axially forwardly andlaterally outward directions to produce a semitoroidal crater having amedian crater diameter approximately coextensive with the diameter ofthe tube in the surface of a metal target plate disposed adjacently andnormally to the front end of the tube at the time the charge isexploded.

c. said charge being made of an explosive material of such a characterthat it produces a time distribution of dynamic explosive loadingeffects by which the high level of explosive loading is sustainedmomentarily after formation of the semitoroidal crater to produce apunchlike explosive loading upon the surface of the target plateencircled by the crater tending to cause an approximately frustoconicalfracture surface extending from the bottom of the crater to the oppositeside of the plate and divergent in the direction toward said oppositeside, whereupon the portion of the plate encompassed by the crater andfracture surface is removed from the body of the plate.

2. A device in accordance with claim 1, wherein said charge is made of acomposition C-type explosive material.

3. A device in accordance with (12) claim 1,

e. said body of revolution, at its forwardmost end, having a substantialcross-sectional area.

4. A device in accordance with claim 3 and further for delivering afollow-through projectile through the perforation left in the platestructure, said device further comprising;

f. said body of revolution having formed therein an axial bore forcontaining a follow-through projectile for delivery through theperforation in the metal plate under force of explosion, said bore atits front end forming a central opening in said substantialcross-sectional area, and

g. a follow-through projectile disposed in said bore.

5. A device in accordance with claim I, and

h. said body of revolution forming a sharp tip at its forwardmost end.

1. An explosive device for removing a circular pluglike fragment from ametal plate structure, comprising; a. cylindrical metal outer casingtube having front and rear ends and containing a charge of explosivematerial, b. said charge having a first, cylindrical, axial portion incircumferential contact with the inner surface of the wall of said tubeand extending forwardly to a circular forward limit of explosive chargeand tube contact, and having a second, front end, axial portionadjoining and extending forwardly from said circular forward limit andterminating at its forwardmost portion at an axial positionsubstantially coadjacent the front end of the tube, said front end axialportion forming an axially aligned forwardly converging body ofrevolution having its outer surface in radially spaced relationship tothe wall of the tube defining an annular cavity thereabout between thebare outer surface of the explosive material and the inner surface ofthe wall of said tube, said annular cavity being of forwardly increasingcross section forming an explosive pressure focusing cavity forconcentrating the initial explosive effect in axially forwardly andlaterally outward directions to produce a semitoroidal crater having amedian crater diameter approximately coextensive with the diameter ofthe tube in the surface of a metal target plate disposed adjacently andnormally to the front end of the tube at the time the charge isexploded. c. said charge being made of an explosive material of such acharacter that it produces a time distribution of dynamic explosiveloading effects by which the high level of explosive loading issustained momentarily after formation of the semitoroidal crater toproduce a punchlike explosive loading upon the surface of the targetplate encircled by the crater tending to cause an approximatelyfrustoconical fracture surface extending from the bottom of the craterto the opposite side of the plate and divergent in the direction towardsaid opposite side, whereupon the portion of the plate encompassed bythe crater and fracture surface is removed from the body of the plate.2. A device in accordance with claim 1, wherein said charge is made of acomposition C-type explosive material.
 3. A device in accordance with(12) claim 1, e. said body of revolution, at its forwardmost end, havinga substantial cross-sectional area.
 4. A device in accordance with claim3 and further for delivering a follow-through projectile through theperforation left in the plate structure, said device further comprising;f. said body of revolution having formed therein an axial bore forcontaining a follow-through projectile for delivery through theperforation in the metal plate under force of explosion, said bore atits front end forming a central opening in said substantialcross-sectional area, and g. a follow-through projectile disposed insaid bore.
 5. A device in accordance with claim 1, and h. said body ofrevolution forming a sharp tip at its forwardmost end.